Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B

The 1883 Explosion of Krakatoa and the Speed of Sound
Thomas Gabrielson
Penn State University

On 27 August 1883, the island of Krakatoa was virtually destroyed by an immense volcanic explosion. The explosion generated a pressure wave that was recorded by more than 50 weather stations worldwide. Several of these stations recorded as many as seven passages of the wave as it circled the earth over the following five days. The distribution of weather stations around the world was sufficient to reconstruct the wave front and its evolution over several days including its distortion by global wind patterns. In 1697, Isaac Newton published his theory for the speed of sound but measurements several years later by a country rector showed that the actual speed of sound was 15% higher than Newton’s prediction. This discrepancy was not resolved for more than a century. The observations from Krakatoa fueled a new fire: the average apparent speed of the Krakatoa pressure wave was close to the speed of sound but was it really a very low frequency sound wave? Some argued that the Krakatoa wave was an atmospheric tsunami – effectively a surface wave riding on the atmosphere. This argument stimulated analysis of waves in the atmosphere for which both compressibility and buoyancy play significant roles. This talk will summarize measurement of the explosion’s wave (including an animation of the wavefront progression over five days) and discuss its impact on understanding the speed of waves in the atmosphere.

Friday, 17 September 2010
Globe Room, Elvey Building
3:45 PM